Hot Corrosion Performance of Super Co-605 at Different Temperatures

Hot Corrosion Performance of Super Co-605 at Different Temperatures

Vinay Kumar Sahu

Assistant Professor, Mechanical Engineering Department Parthivi College of Engineering & Management

Bhilai-3 (C.G.) , India

Swapnil Shukla

Assistant Professor, Mechanical Engineering Department Parthivi College of Engineering & Management

Bhilai-3 (C.G.) , India

Pradeep Chandra

Assistant Professor, Mechanical Engineering Department

Parthivi College of Engineering & Management Bhilai-3 (C.G.) , India

Abstract -The major degradation mechanism occurrences found due to oxidation and hot corrosion which is highly responsible for failure of parts of boiler and gas turbines. These failures occur because of the wide range usage of the fuels such as oil, coal at increased temperatures. In current investigation Hot corrosion performance of bare SuperCo-605 has been evaluated with aggressive environment. For aggressive environment composition of sodium sulphate and vanadium pentaoxide have been mixed in proper ratio (Na2SO4+60%V2O5) to provide an experimental condition under cyclic conditions at an elevated temperatures of 8500C & 9500C. The kinetics of the corrosion is approximated by weight change measurements made after each cycle the total duration of experimental is up to 50 cycles. Each cycle consists of keeping the samples for 1 hour duration in Kanthol wire tube furnace at 8500C and 9500C followed by 20 minute cooling in ambient air. Weight change data has been taken after each cycle by digital electronic balance machine with an accuracy of 1 milligram. Graphs have been plotted between weight gains per surface area to number of cycles. SuperCo-605 has shown poor performance in hot corrosion environment as the temperature increased. It suffered from intensive spallation in the form of removal of scales.

Keywords-Oxidation, Hot Corrosion, Spallation.

1. INTRODUCTION

   Boiler & Gas turbine components and blades and other important engineering devices or systems operating at high elevated temperature. Due to this high temperature they may be fail and it concluded that high-temperature oxidation and hot corrosion are the main failure modes of components in the hot sections of gas turbines, boilers etc [1]. Corrosion is deterioration of material or unwanted wear or scale formation on to the surface of material. Oxidation is the corrosion reaction which placed due to high-temperature, which occurs when metals or alloys are heated in oxidizing environments such as with access of air and oxygen. Metals and alloys sometimes experience accelerated oxidation when their surfaces are covered with a thin film of fused salt in an oxidizing gas atmosphere at elevated temperatures. This is known as a hot corrosion where a nonprotective oxide scale is formed at the surfaces [2]. Basically Hot corrosion is the

   result of attack by fuel and/or ash compounds of Na, Cl, V, and Sodium l that are present in the coal or in fuel oil used for combustion in the mentioned applications. Residual fuel oil contains some sodium, sulphur and vanadium as impurities, which form compounds such as Na2SO4 (melting point 8840C), V2O5 (melting point 6700C), and complex vanadates by reactions in the combustion systems [1]-[3]. These compounds, known as ash, deposit on the surface of materials and induce accelerated oxidation (hot corrosion) [4]-[6].

2. METHODOLOGY

   A. Substrate material

   The SuperCo-605 has been selected for study the nominal chemical composition of substrate material is reported in table 2.1.

   TABLE I NOMINAL COMPOSITION OF SUPERCO-605

   Material	Cr	Fe	W	Mn	C	Si	Ni	Co
   SuperCo- 605	20	3	15	1.5	.08	.03	10	Bal

   B .Substrate preparation and Coating formulation

   The specimens, with dimensions of 20 × 15 × 5 mm3, were cut from the alloy sheet of SuperCo-605. The specimens polished by the using of emery papers with the size of 180, 220, 400, 600 grit numbers. Subsequently the specimens were washed properly, with the use of acetone and dried in hot air to remove any moisture.

   1. Air and molten salt corrosion test

      Cyclic studies were performed for the steel substrates in molten salt environments (Na2SO460% V2O5) and in air for 50 cycles. A Salt deposition of uniform thickness with in limit of 3 to 5 mg/cm2 of (Na2SO460% V2O5) were applied with a camel hair brush on the preheated sample (250°C) after that heat them up to 3-4 hrs for proper adhesion of salt. Each cycle consisted of 1 h of heating at 850°C & 9500C in a

      Kanthol wire tube furnace followed by 20 min of cooling at room temperature. The purpose of imposing cyclic conditions was to create an accelerated environment as observed in real cases for hot corrosion testing. The weight change measurements were taken at the end of each cycle using an electronic balance machine with a sensitivity of 1 mg. [7, 8]

   2. Experimental condition

   TABLE II EXPERIMENTAL CONDITIONS

   Material	Temp- erature	Environ- ment	Time
   			50 cycle of 1 hrs
   SuperCo-	8500C	Na2SO4+	heating followed
   605	9500C	60% V2O5	by 20 min cooling in ambient air

3. RESULT & DISCUSSION

   Hot Corrosion performance has been tested and for each cycle and weight change has been measured. This weight change is in milligram and for result we divide it by surface area of used boiler steel for testing. After this plot a graph between Number of cycle and Weight change (mg/cm2). Following graph has been plotted after complete 50 cycles for each condition.

   20

   Weigh gain (mg/cm2)

   Weigh gain (mg/cm2)

   15

   10

   5 Uncoated

   0

   0 20 40 60

   Number of Cycle

   Fig 3.1 Hot corrosion behaviour of SuperCo-605 at 8500C

   Fig 3.2 Corrode material 9500C and 8500C

   35

   30

   25

   20

   15

   10

   5

   0

   Uncoated

   35

   30

   25

   20

   15

   10

   5

   0

   Uncoated

   0 20 40 60

   Number of cycle

   0 20 40 60

   Number of cycle

   Weight gain (mg/cm2)

   Weight gain (mg/cm2)

   Fig 3.3 Hot corrosion behaviour of SuperCo-605 at 9500C

   A. Hot Corrosion performance

   Weight gain (mg/cm2)

   Weight gain (mg/cm2)

   SuperCo-605 Weight gain at 8500C is 15.79 mg/cm2 and at 9500C is 32.28 mg/cm2 up to 50 cycles. It shows that approximate twice more weight gain due to increase in temperature up to 50 cycles for hot corrosion.

   35

   30

   25

   20

   15

   10

   5

   0

   850C

   950C

   35

   30

   25

   20

   15

   10

   5

   0

   850C

   950C

   0 20 40 60

   Number of cycle

   0 20 40 60

   Number of cycle

   Fig 3.4 Comparison of hot corrosion performance at 8500C and 9500C

4. CONCLUSION

In the present investigation, oxidation and hot corrosion tests of SuperCo-605 have been carried out at the temperatures of 8500C & 9500C. Following conclusions are drawn:

• As we increasethe temperature so those corrosion rates also increase.

• SuperCo-605 performance is low for corrosive environment because there is spallation behavior appears in cycles up to 50 cycles…

• Hot corrosion shows badly effect on super alloy with approx twice as we temperature increase.

ACKNOWLEDGMENT

The authors are very much thankful to Mr. K Ramesh, General Manager (Commercial), and Mr. I S N Murthy, Mishra Dhatu Nigam Limited, Hyderabad (India), for providing the Superalloy and we also want to say thanks our Supervisor Dr. S.B.Mishra for supporting us.

REFERENCES

[1]. H. Singh, D. Puri and S. Prakash , Advance Material Science ,Vol. 16

, pp. 27-50,2007

[2]. R. A. Rapp and Y. S. Zhang,Corrosion Science, Vol . 47, pp. 67- 72,1994

[3]. K.L. Luthra, H.S. Spacil, J. , Electrochem. Soc Vol. 129 , pp. 649, 1982

[4]. N. Eliaz, G. Shemesh, R.M. Latanision , Engg. Fail. Analysis. Vol. 9

, pp. 31-33, 2002

[5]. T. S. Sidhu, S. Prakash, R.D. Agrawal, Material Science & Engg.,

Vol No. 445, pp. 210-218,2007

[6]. Subhash kamal , R ayaganthan and S prakash , Material Science,Vol. 33, , pp. 299306, 2010

[7]. Deepa Mudgal , Surendra Singh and Satya Prakash, Minerals and materials characterization & engineering, Vol No. 11, pp. 211- 219,2012

[8]. K.L. Luthra, , Metallurgical of transaction Vol No. 13 A, pp. 114- 118, 1982